One of the main challenges involving polymer materials lies in the development of increasingly light components with improved properties for use in applications such as food packaging or the automotive industry. A possible strategy combines weight reduction by foaming of a base material with the incorporation of reinforcing and/or functional fillers acting as cell nucleants or promoters. Cell nucleating agents are commonly used in polymeric foaming processes to enhance cell nucleation. With the presence of nucleating agents, heterogeneous nucleation becomes the predominant mode of cell nucleation during polymer foaming processes.
Polypropylene foams are known in the art, but they have reduced stiffness and mechanical strength compared to conventional polypropylene. Increasing oil prices have contributed to increased production costs of plastic resins and finished plastic products. Since plastic resin costs typically amount to 50 to 60% of the total cost of any given plastic product, a reduction of resin amounts in plastics while at the same time maintaining mechanical and other properties of the plastic products is of considerable economic benefit.
WO 2010/065053 A1 describes the use of cell nucleating compositions in the production of polyhydroxyalkanoate foams. A wide range of nucleating agents were used, including a high aspect ratio talc (FlexTalc® 610D). Polyhydroxyalkanoates are biodegradable polymers and mainly of interest for the production of biodegradable films for food packaging. No indications of the properties of the foams obtained, when compared to the unfoamed products are disclosed.
KR 10-0837106 B1 discloses a method for preparing non-crosslinked polypropylene foamed sheets comprising the steps of extruding a mixture 93 to 98 parts by weight of a polypropylene homopolymer with up to 3 parts per weight talc, followed by foaming by injection of 1 to 4 parts by weight of butane gas as a foaming agent. There is no indication regarding the physical properties (such as density, mechanical strength or stiffness) of the finished product.
KR 10-2007-0028736 A discloses rigid foams for automotive interior materials prepared from a composite resin prepared by melt-mixing 5 to 10 parts by weight of a talc with an average particle size of 10 to 13 μm and 0.1 to 0.4 parts by weight of an antioxidant with 100 parts by weight of a resin mixture comprising 90 to 95 parts by weight of a polypropylene resin.